Incident Chronology at TMI from NRC: 1979-2014

March 28, 1979, 4:00 a.m. - Beginning of the Three Mile Island (TMI) Unit-2 loss-of-coolant, core melt accident. The plant came within 30 minutes of a full meltdown. The reactor vessel was destroyed, and large amounts of unmonitored radiation was released directly into the community.

March 28, 1979, 4:30 p.m. - Press conference of Lt. Governor William Scranton:
This is an update on the incident at Three-Mile Island Nuclear Power Plant today. This situation is more complex than the company first led us to believe. We are taking more tests. And at this point, we believe there is still no danger to public health. Metropolitan Edison has given you and us conflicting information. We just concluded a meeting with company officials and hope this briefing will clear up most of your questions. There has been a release of radioactivity into the environment. The magnitude of this release is still being determined, but there is no evidence yet that it has resulted in the presence of dangerous levels. The company has informed us that from about 11 a.m. until about 1:30 p.m., Three-Mile Island discharged into the air, steam that contained detectable amounts of radiation.

March 30, 1979 - Governor Richard Thornburgh recommended an evacuation for preschool children and pregnant women living within five miles of the plant. Out of a target population of 5,000, over 140,000 Central Pennsylvanians fled the area. Schools in the area closed...

The U.S. House of Representatives committee examining reporting information during the accident concluded:

The record indicates that in reporting to State and federal officials on March 28, 1979, TMI managers did not communicate information in their possession that they understood to be related to the severity of the situation. The lack of such information prevented State and federal officials from accurately assessing the condition of the plant. In addition, the record indicates that TMI managers presented State and federal officials misleading statements (i.e. statements that were inaccurate and incomplete) that conveyed the impression the accident was substantially less severe and the situation more under control than what the managers themselves believed and what was in fact the case.